1. Field of the Invention
The present invention relates to a motorcycle particularly of scooter-type provided with an article accommodation (storage) box having large inner volume capable of accommodating a helmet or like, the article accommodation box being disposed below a rider's seat.
2. Related Art
A scooter-type motorcycle of the above structure is known, for example, from Japanese Patent Laid-open (KOKAI) Publication No. 2001-138975 or No. HEI 2-92791 (92791/1990). One example of such scooter-type motorcycle is, for example, shown in FIG. 4.
With reference to FIG. 4, the scooter-type motorcycle is provided with a power unit 104, including an engine 101 and a power transmission 102, which is vertically swingable together with a rear wheel 103. Such power unit 104 is disposed below an article accommodation box (or article storage chamber) 105. A cylinder 107 of the engine 101 extends forward from a front surface side of a crank case 106 of the engine 101 at a portion directly below the bottom surface 105a of the article accommodation box 105. A rider's seat 108 is disposed above the article accommodation box 105 to be openable about a rotational shaft 108a. In FIG. 4, reference numeral 109 denotes a helmet disposed in the accommodation box 105.
In the conventional structure of the scooter-type motorcycle, such as shown in FIG. 4, the engine 101 is generally arranged below the rider's seat 108 in consideration of the structure of the motorcycle body, and therefore, a two-stroke-cycle engine is mainly mounted in an attitude as low as possible by almost horizontally laying the cylinder.
In recent years, however, a four-stroke-cycle engine has been mainly employed in view of environmental matters. In the four-stroke-cycle engine, an oil stored in a bottom portion of the crank case 106 is supplied to the cylinder (i.e., cylinder head) 107 by means of oil pump, and the oil circulation from the cylinder 107 to the crank case 106 is performed through dropping due to the gravity. Because of this reason, in order to facilitate the oil circulation, the cylinder 107 has a front side portion extending obliquely upward in comparison with the arrangement in the two-stroke-cycle engine.
However, in the arrangement that the cylinder 107 extends forward from the front surface side of the crank case 106 at the portion directly below the bottom surface 105a of the article accommodation box 105, if the cylinder 107 is arranged with the front side portion thereof extending forward with an upward inclination in consideration of the well oil circulation, there may cause a fear that the cylinder 107 interferes with the bottom surface 105a of the accommodation box 105.
In order to obviate such fear, it will be necessary to arrange the accommodation box 105 so that the bottom surface 105a thereof is positioned at a higher level or to dispose both the accommodation box 105 and the rider's seat to be higher in its level in their entire structure, which adversely results in the reduction of the inner volume of the article accommodation box 105 or deterioration of the riding condition, footing condition or like of the motorcycle.
Moreover, on the upper surface portion of the crank case 106, there are disposed a swing shaft 111 being a center of pivotal movement of the power unit 104, a starter motor 112 for the engine operation, an intake device 113 of the engine and so on, and accordingly, it is necessary to consider the interference of these members with the bottom surface 105a of the article accommodation box 105. That is, it is obliged to pay attention to the arrangement of the members on the crank case 107 (i.e., the power unit 107) and the entire shape or size of the article accommodation box 105.